Amplification Circuit and Hearing Aid

ABSTRACT

Certain embodiments of the present technology provide improved amplification circuits and hearing aids that can utilize such amplification circuits. In an embodiment, for example, an amplification circuit includes: a first sub circuit configured to create a voltage drop when a supply voltage is above a first voltage; and a second sub circuit configured to create a reverse voltage drop when the supply voltage is below a second voltage, wherein the first and second sub circuits operate to maintain idling current within a range. Certain embodiments of the present technology also provide hearing aids that include removable dampers.

RELATED APPLICATIONS

This application makes reference to the U.S. Patents identified below,which patents are hereby incorporated herein by reference in theirentirety:

-   U.S. Pat. No. 3,588,383, filed Feb. 9, 1970;-   U.S. Pat. No. 3,701,865, filed Jun. 25, 1971;-   U.S. Pat. No. 4,170,720, filed Mar. 3, 1978;-   U.S. Pat. No. 4,592,087 filed Dec. 8, 1983;-   U.S. Pat. No. 4,689,819 filed Mar. 19, 1986;-   U.S. Pat. No. 4,852,683, filed Jan. 27, 1988;-   U.S. Pat. No. 5,131,046, filed Nov. 3, 1989-   U.S. Pat. No. 5,113,967, filed May 7, 1990;-   U.S. Pat. No. 5,144,675, filed Mar. 30, 1990;-   U.S. Pat. No. 5,887,070, filed Dec. 19, 1996;-   U.S. Pat. No. 6,666,295, filed Jan. 23, 2001; and-   U.S. Pat. No. 6,830,876, filed Nov. 10, 2003.

This application also makes reference to the U.S. patent applicationSer. No. 11/031,915, filed Jan. 7, 2005 and published as 2005/0147267,which patent application is hereby incorporated herein by reference inits entirety.

UNITED STATES PATENT FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[Not Applicable]

MICROFICHE/COPYRIGHT REFERENCE

[Not Applicable]

BACKGROUND OF THE INVENTION

Despite the availability of technically advanced hearing aids, some ofwhich are fully digital hearing aids, up to 80% of individuals whoadmittedly need hearing aids do not obtain them.

This has been true even though high-fidelity hearing aids arecommercially available. One example of such a hearing aid is the K-AMP®hearing aid, elements of which are described, for example, in U.S. Pat.Nos. 4,170,720 and 5,131,046, and 5,144,675. Experimental testing hasindicated that the K-AMP® hearing aid provides a fidelity that exceedsother digital or analog hearing aids. One measure of K-AMP® hearingaid's fidelity is that four members of the Chicago SymphonyOrchestra—including a former concertmaster of the CSO and the principalof the 2^(nd) violin section of the CSO—wore K-AMP® hearing aids onstage and off until they retired a few years ago. At one time, anestimated 18-20% of all hearing aids in the U.S. were K-AMP® hearingaids. As one internationally known professor stated: the K-AMP® “had anincredible and indelible worldwide influence on how hearing aids shouldbe designed, selected and fitted” (Gus Mueller, Ph.D., quoted inEtymotic Research: 25 Years of Research & Product Development for theEar, 2008). Unfortunately, K-AMP® hearing aids have required relativelyexpensive Class D amplifiers and receivers in order to provide theirhigh-fidelity performance at high input levels. Examples of such Class Damplifiers and receivers are described, for example, in U.S. Pat. Nos.4,592,087 and 4,689,819, issued to Killion.

Experimental testing has shown that the highest intelligibility in noisewas obtained with hearing aids judged to have the highest sound quality,both by those with normal hearing and those with hearing loss (flat orsloping). In fact, the highest intelligibility was the natural sound ofthe open ear, which provided better fidelity and better intelligibilityin noise than roughly half of the second-generation digital aids oftendescribed (inaccurately) as having “CD quality.” Experimental datasupporting this finding is shown in FIG. 1A, which is a reproduction ofFIGS. 7 and 8 from Killion M C, “Myths that Discourage Improvements inHearing Aid Design,” The Hearing Review, 11, No. 1, 32-40, 70 (2004).The validity of these fidelity ratings is illustrated in FIG. 1B, wherethe fidelity rating listeners gave to the sound of some digital hearingaids is compared to the “25-Band Accuracy Score” calculated from thefrequency response as described by Killion in 1979 (reference 8 in the“Myths” paper given above). Other experiments have attempted to rate thedollar value of the sound of some digital hearing aids. The soundquality of the majority of these aids was rated as being worth much lessthan their typical cost of $2,000-$3,000 each, as shown in FIG. 1C takenfrom the same paper. Dollar value for music reproduction is only onedimension in hearing aid value of course, but the relationship shownabove between intelligibility in noise and fidelity suggests that partof the reason for hearing aids remaining in dresser drawers (i.e., goingunused) may be unsatisfactory sound quality.

Nonetheless, the question of why 80% of those who need hearing aids gowithout them remains unanswered. There are many stated reasons for thisphenomenon. Among them are: (1) a friend or relative purchased a hearingaid that ended up in a dresser drawer because it did not live up to thebuyer's expectations; (2) the person needing a hearing aid didn't wantto see a licensed professional (a licensed professional dispensinghearing aids is required by regulations in all but two states); and/or(3) a hearing aid was considered too expensive to afford, or simply tooexpensive. For example, one may hear comments such as “I can buy atop-of-the-line refrigerator for a few hundred dollars. Why should Ihave to pay more for a hearing aid?”

Whatever the reason, about 24 million people are going without hearingaids. Unfortunately, those persons and their friends and relativessuffer the consequences. As one author stated, “No one goes withouthearing aids—they simply force their spouse to holler at them.” Thismakes for less than friendly and loving conversations: It is hard tofeel warm and fuzzy when someone is shouting at you. And it is hard tofeel warm and fuzzy when you have to shout at them. Emotions aside, thecost of unaided hearing loss has been estimated to be $2,500 annually inincome for those with mild-moderate hearing loss and $5,600 annually forthose with moderate loss (Sergei Kochkin, “The impact of untreatedhearing loss on household income”). Nationally, this is perhaps $50billion dollars in lost income.

Of the three reasons listed above for not buying hearing aids, the firstcan be handled by improving the sound quality of hearing aids and—mostimportant—making every effort to induce expectations that are consistentwith what the person will experience. In many cases, the person who doescome in for hearing aids has two problems: inability to hear quietsounds, and inability to hear in loud restaurants and the like. Thefirst can be solved completely for most persons with most hearing aids.The second, when severe, can be solved by use of a remote FM or othermicrophone near the talker, where the signal-to-noise ratio at themicrophone can be 20 dB better than at the listener's hearing aidmicrophone. A detailed discussion of “SNR loss” is beyond the scope ofthis application, but some 20% of all hearing aid wearers havesufficient SNR loss so they cannot understand speech in a noisyrestaurant or cocktail party with or without their hearing aids. (Somereport they hear better in those environments when they take theirhearing aids off: It is so loud that everything is already audible, andtheir hearing aids make things even harder to understand.) If the prettypictures and advertising copy lead people to expect they will hearbetter in noise with their hearing aids, those with severe SNR loss willsurely be disappointed. Various lecturers have suggested that asatisfied person tells three other people, but a dissatisfied persontells 13 (one recent book title suggested a larger ratio: PeterBlackshaw, “Satisfied Customers Tell Three Friends, Angry Customers Tell3,000).” To the extent that these ratios apply to hearing aidpurchasing, even 20% of hearing aid purchasers may be sufficient todiscourage a large portion of the 80% who don't purchase hearing aids.Industry statistics indicate some 15% of hearing aids are returned forcredit as unsatisfactory to the purchaser. Some estimates indicate thatanother 14% end up in dresser drawers (Sergei Kochkin, “The VA andDirect Mail Sales Spark Growth in Hearing aid Market,” Hearing Review,December 2001).

Fortunately, it is not hard to prominently state in the description of ahearing aid that those with severe loss of ability to hear in noise willbe able to hear quiet sounds better, but will need additional assistancein noisy surroundings. To the applicant's knowledge, no hearing aidadvertisements make such a candid statement, but it is certainly just asappropriate for a low-cost hearing aid as for a hearing aid costing$3,000.

The second and third reasons for not obtaining hearing aids (need to seea professional and high cost) can be taken care of simultaneously, sincethe majority of the cost of hearing aids is the cost of the professionaldispensing process. Before discussing the cost of a traditional hearingaid, it should be stated that this discussion is not in any way meant todisparage that process. There is no question that the means to the bestpossible hearing aid fitting is to see someone who understands hearingand hearing aids, and has demonstrated this understanding in the processof obtaining advanced degrees and a dispensing license. And much of the“soft” part of the dispensing is the teaching—which can only be donefirst hand—of the fact that the brain will “rewire” to accommodate theinitially unnatural sound of the hearing aid and the fact that anychange to the auditory input may make it sound to some new wearers as ifthey are listening to speech in a sea of noise. Not to mention simplyputting the battery in right, which can be a major challenge for somepersons. In good hands, the process is skilled, caring, and even so mayrequire one or more readjustments of the hearing aid response orprocessing.

In traditional hearing aid fitting, there are two components to the“fitting” process: Taking impressions and obtaining an earmold (usuallybut not always custom) fitted to the external ear, plus adjusting theanalog or digital signal processing to compensate for the individualcharacteristics of the hearing loss, for example, “flat loss”(approximately the same loss at all frequencies), “high frequency loss”(significantly greater loss at high frequencies than at lowfrequencies), “ski slope loss” normal or near normal low-frequencyhearing with precipitous drop to moderate-severe high-frequency loss,etc. In the normal fitting of a hearing aid, the frequency response ofthe hearing aid is adjusted at each level to compensate for the loss atthat level. Various “fitting formulae” have been developed to provideappropriate targets based on the shape and degree of the hearing loss.One such popular fitting target called FIG. 6 was developed by applicantKillion.

These two fitting processes typically require two or three visits andthe attention of licensed skilled professionals, often with doctoratedegrees. The advantage of the traditional fitting method is a betterfitting than may be obtained in a one-size-fits-many ready-fit hearingaid design. The disadvantage is cost: The total cost of the basichearing aid itself plus the professional fees typically add up to $3,000to $8,000 for a pair of hearing aids.

For those who won't see a professional for a traditional hearing aid,however, the above advantages are never experienced: the person iswithout amplification. For such individuals, an inexpensive hearing aidthat is simple to use, especially if a trial purchase is encouraged byallowing the purchaser to return the aid if they are not satisfied, mayencourage a trial of hearing aids. Moreover, it seems likely that afterexperiencing the improved audibility of too-quiet sounds, those withsufficient resources may well be inclined to see a professional for evenbetter hearing aids.

Interestingly enough, applicant Killion has had two recent conversationsthat suggest cost can be the deciding factor even when adequate fundsare available. At the Oshkosh, Wis., EAA air show, a conversation arounda picnic table with four pilots in their 60s and 70s indicated that allfour could use hearing aids but had never gone to get them. When thediscussion of a high-quality ready-fit hearing aid for $300 came up, allwere interested and two said eagerly “tell me where I can get one.” Allwould try a do-it-yourself $300 hearing aid, yet none planned to go geta $3,000 hearing aid. Each of these men owned, or had previously owned,private airplanes costing in excess of $100,000. Similarly, atChautauqua, N.Y., Institution, where the cost of registration,transportation and lodging for a week typically exceeded $2,500, aconversation around another picnic table with four high-intellect womenin their 60s and 70s (one perhaps in her 80s) indicated that, again, allcould benefit from hearing aids, but did not intend to go get one. Yetall were keenly interested in a $300 hearing aid of good quality (evenif it didn't have all the digital features so popular today).

After concluding that cost and “seeing a professional” were majorfactors in discouraging many persons from seeking hearing aid help,applicant Killion, who has taught the advanced hearing aidelectroacoustics course to Northwestern University audiological graduatestudents for 25 years, and his colleague, Dr. Gail Gudmundsen, who hasdispensed over 10,000 hearing aids over the years, applied to the FDAfor creation of a new category of hearing aid that can be purchased overthe counter (“OTC”). See,http://webreprints.djreprints.com/1257230721151.html, Wall StreetJournal. These OTC hearing aids were meant to be self-fitted by theself-selection of eartips, much as applicant Killion's company'shigh-fidelity earphones are fitted by the user as described, forexample, in U.S. Pat. No. 5,887,070, entitled “High fidelity insertearphones and methods of making same,” issued to Iseberg et al., and onthe Internet at http://www.etymotic.com/ephp/epcomp.aspx. Theapplication to the FDA was denied, but the problem remains unsolved.

Applicant Killion has published three papers summarizing many probablereasons for hearing aid failure, but certainly the unnatural sound ofmany aids appears to be an important one. See Killion M C, “Myths thatDiscourage Improvements in Hearing Aid Design,” The Hearing Review, 11,No. 1, 32-40, 70, 2004; Killion M C, “Myths About Hearing in Noise andDirectional Microphones,” The Hearing Review, 11, No. 2, 14-19, 72-73,2004, and Killion M C, “Myths about Hearing Aid Benefit andSatisfaction,” The Hearing Review, 11, No. 8, 14-20, 66, 2004.

All of these considerations suggest that a low-cost one-size-fits-manyhearing aid might result in substantially improved lives for many ofthose who don't presently obtain hearing aids but need them, especiallyif it minimized the need for several weeks of brain rewiring required toget used to the unnatural sound of some digital hearing aids.

A principle limitation has been the unavailability of a low-power outputcircuit compatible with the analog bipolar circuit used in K-AMP®hearing aids, which have required more costly Class D circuits. Also,while digital hearing aid circuits have employed switching outputscomparable in efficiency to Class D switching outputs, the overheadcurrent for digital circuits is large, wiping out the possible advantageto the switching output. Finally, battery life of many digital hearingaids is only one week and that of many Completely In the Canal (“CIC”)hearing aids is often only 3 days.

Thus, there is a need for a low-cost hearing aid that exhibitsacceptable performance characteristics including improved sound qualityand extended battery life.

BRIEF SUMMARY OF THE INVENTION

Certain embodiments of the present technology provide improvedamplification circuits and hearing aids that can utilize suchamplification circuits. Certain embodiments of the present technologyalso provide hearing aids that include removable dampers.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A depicts graphs relating to myths that discourage improvements inhearing aid design.

FIG. 1B depicts a graph comparing average fidelity ratings assignedseveral hearing aids and other sound reproducers compared with afrequency response 25-band Accuracy Score calculated for the same soundreproducers.

FIG. 1C depicts a graph comparing value ratings of hearing aids bynormal hearing individuals and hearing impaired individuals.

FIG. 2A depicts a prior art amplification circuit.

FIG. 2B depicts the calculated idling current as a function of supplyvoltage in the prior art amplification circuit shown in FIG. 2A.

FIG. 2C depicts a prior art amplification circuit.

FIG. 2D depicts current in the prior art amplification circuit shown inFIG. 2C.

FIG. 3 is a diagram depicting an amplification circuit in accordancewith an embodiment of the present technology.

FIG. 4 is a diagram depicting hearing aid components and circuitry usedin accordance with an embodiment of the present technology.

FIG. 5A is a diagram depicting hearing aid components used in accordancewith an embodiment of the present technology.

FIG. 5B is a diagram depicting hearing aid components used in accordancewith an embodiment of the present technology.

FIG. 6A is a top view of a hearing aid used in accordance with anembodiment of the present technology.

FIG. 6B is a side view of the hearing aid shown in FIG. 6A.

FIG. 6C is a side view of the hearing aid shown in FIG. 6A.

FIG. 6D is a side-sectional view of the hearing aid shown in FIG. 6A.

FIG. 6E is a side view of the hearing aid shown in FIG. 6A with aneartip attached thereto.

FIG. 6F is a side view of an eartip used in accordance with anembodiment of the present technology.

FIG. 6G is a side sectional view of the eartip shown in FIG. 6F.

FIG. 6H is a side view of an eartip used in accordance with anembodiment of the present technology.

FIG. 6I is a side sectional view of the eartip shown in FIG. 6H.

FIG. 6J is a side view of a hearing aid used in accordance with anembodiment of the present technology.

FIG. 6K is a side sectional view of the hearing aid shown in FIG. 6Jwithout the eartip attached thereto.

FIG. 6L is a graph comparing results of frequency response experiments.

FIG. 7A is a top view of a hearing aid used in accordance with anembodiment of the present technology.

FIG. 7B is a side view of the hearing aid shown in FIG. 7A.

FIG. 7C is a side view of the hearing aid shown in FIG. 7A.

FIG. 7D is a side-sectional view of the hearing aid shown in FIG. 7A.

FIG. 7E is a side view of the hearing aid shown in FIG. 7A with aneartip attached thereto

FIG. 7F is a side view of a hearing aid used in accordance with anembodiment of the present technology.

FIG. 7G is a side sectional view of the hearing aid shown in FIG. 7Fwithout the eartip attached thereto.

FIG. 8A illustrates a one-size-fits-most hearing aid in accordance withan embodiment of the present technology.

FIG. 8B illustrates a side view of the hearing aid of FIG. 8A with thebattery sleeve retracted.

FIG. 9A illustrates a perspective view of a hearing aid used inaccordance with an embodiment of the present technology.

FIG. 9B depicts the hearing aid of FIG. 9A in an operative position on auser.

FIG. 9C depicts the hearing aid of FIG. 9A and a boom/microphoneassembly that can be used therewith in accordance with an embodiment ofthe present technology.

The foregoing summary, as well as the following detailed description ofembodiments of the present invention, will be better understood whenread in conjunction with the appended drawings. For the purpose ofillustrating the invention, certain embodiments are shown in thedrawings. It should be understood, however, that the present inventionis not limited to the arrangements and instrumentality shown in theattached drawings.

DETAILED DESCRIPTION OF THE INVENTION

Applicants set out to determine if it was possible to incorporate thebipolar transistor circuit utilized in K-AMP® hearing aids in a low-costintegrated circuit. The aforementioned Class D amplifier that was usedin previous K-AMP® hearing aids, was realized with CMOS integratedcircuits, and was relatively expensive. Applicants concluded that abipolar Class B circuit may be capable of being used in connection withthe desired low-cost integrated circuit, however, numerous designchallenges would need to be overcome. As to battery life, in manyinstances, Class B and Class D amplifiers can produce a 7-10 timesincrease in battery life over a Class A amplifier designed with goodfidelity (which many Class A amplifiers are not). See, for example,applicant's Johnson and Killion “Is Class D better than Class B?” Amer.J. Audiology March 1994 11-13, also seehttp://www.etymotic.com/pdf/erl-0027-1994.pdf.

An analysis of previous Class B hearing aid amplifiers was accordinglyundertaken in order to identify problems that can prevent such hearingaid amplifiers from providing satisfactory performance characteristics.

One such previous hearing aid amplifier is described in U.S. Pat. No.3,995,114, entitled “Ultra Low Current Amplifier,” which issued toMarschinke. As shown in FIG. 2A (Marschinke's FIG. 1), a pair oftransistors, one PNP 30 and one NPN 31, is connected in series betweenthe positive supply and ground. By adjusting resistor 33 to provide alow idling current, and using feedback to linearize the operation, alow-distortion Class B push-pull operation could be obtained undercertain conditions. As shown, a large coupling capacitor is required toblock the amplifier's DC bias voltage from being impressed on thereceiver.

By using a second amplifier in a “bridge” configuration with the first,Marschinke was able to connect the receiver between the outputs of thetwo amplifiers and eliminate the need for the large coupling capacitor.This is because the amplifier's DC bias can be impressed onto both sidesof the receiver resulting in a zero bias current condition across thereceiver. Also, this dual amplifier configuration doubles the maximumoutput voltage that can be delivered to the receiver. This means ahigher impedance receiver can be used for a comparable output, thusreducing the required drive current.

However, the Marschinke amplifier exhibits certain characteristics thatcan undermine modern, efficient manufacturing processes. In particular,both the original Marschinke circuit and the two-amplifier bridgeconfiguration suffered from a large change in idling current throughseries transistors 30 and 31. For example, at a supply voltage from cell10 of 1.3 Volts, certain discrete transistors might each have aBase-Emitter voltage of 550 mV at a desired idling current such as 50uA. The difference between the 1.1 Volt sum of those two voltages andthe supply voltage required that resistor 33 be chosen to provide a 0.2Volt drop. With a transistor beta (sometimes called hfe) of 100, theresulting 0.5 uA current would correspond to a value of 400 kOhm forresistor 33. Note that the feedback resistor 44 would provide a DCsignal to transistor 21 and hence to transistor 24 to adjust the voltageat the Bases of the output transistors (30 and 31) to assure that theircollector currents are equal.

Applicants have found that one problem with the Marschinke circuit isthat there is no compensation for the 2.2 mV per degree C. temperaturecoefficient of the Base-Emitter voltages of Transistors 30 and 31. Thus,an increase of 18 deg C. would cause a 40 mV drop in VBE of bothtransistors 30 and 31, which would increase the 200 mV drop acrossresistor 33 and, taking into account the VBE voltage change withcurrent, decrease the idling current approximately 30% above the designnominal. Conversely, a decrease of 18 deg C. would cause a 40 mVincrease in VBE of both transistors, which would decrease the idlingcurrent approximately 30%. However, in connection with Class Bamplifiers, it can be desirable to maintain a stable idling currentacross temperature, device-to-device variations and supply voltage inorder to maintain output capability and low distortion of the class Bamplifier circuit. In some In-The-Ear (ITE) hearing aid applications, acertain amount of temperature dependence may be acceptable since onlythe surface of the hearing aid is exposed and the portion inside the earcanal is maintained at approximately body temperature by contact withthe ear canal. Thus, even with outside temperatures of −18 deg C. (0 degFahrenheit), the hearing aid circuit was unlikely to drop more than 5-10deg C. In Behind The Ear hearing aids, on the other hand, much of thesurface of the hearing aid is exposed and an uncompensated temperaturecoefficient may cause an audible degradation in performance.

Applicants have found that a more serious limitation is the fact thatthe Marschinke circuit has no means to maintain adequate current withbattery voltage fluctuation. In the example above where stable operationhas been obtained at 1.3 V (1300 mV) and resistor 33 in FIG. 2A ischosen to produce an idling (no signal) current of 50 uA, a fresh cellproviding 1.4 V would increase the calculated idling current to 70 uA,as shown in FIG. 2B. Further, when the battery voltage drops to 1.1Volt, the calculated idling 15 uA current in transistors 30 and 31 wouldprovide a high-crossover-distortion operation. If the supply voltagedrops to 1 V (1000 mV), the calculated idling current drops to 10% ofthe nominal value: the available idling current would be too low toprevent severe crossover distortion.

A farther disadvantage of the Marschinke circuit is its use of a Class Adriver (transistor 24) to supply drive to the output transistors 30 and31, such that the driver transistor 24 would have an idling currentcomparable to the output stage in order to provide sufficient drive tothe output transistors 30 and 31.

At some point, hearing aid amplifiers moved to a push-pull circuitdesigned to drive three-terminal receivers as shown in FIG. 2C. In suchcircuits, the receiver coil is alternatively energized by Q101 and Q102,producing alternatively the current IA in the collector of Q101 and IBin the collector of Q102. These currents are plotted in FIG. 2D for asine wave output. Since each half of the receiver coil has the samenumber of turns and is alternately energized, the result is equivalentto a continuous sine wave current IC in either coil. The circuit of FIG.2C exhibited higher quiescent current and used a more expensivereceiver, but the amplifiers had fewer production issues than theMarschinke circuit. In addition to the typically higher idling current,the Class B circuit of FIG. 2C is less efficient than a circuit using atwo-terminal receiver. This comes about because only one half of thereceiver coil is energized in each signal swing. Each half of thereceiver coil must of necessity take up only half of the available spacefor the receiver coil. The result is that the DC resistance of eachactive half coil must be twice the resistance of a simple coil havingthe same number of turns filling the available space.

The importance to efficiency of minimizing coil resistance isunderstandable when the receiver is to be used in a Class D applicationsuch as those described in U.S. Pat. Nos. 4,592,087 and 4,689,819, bothentitled “Class D Hearing Aid Amplifier,” and both issued to Killion.Such applications have a theoretical 100% efficiency. The principlecomponent of idling current in a Class D hearing aid application is thecurrent flowing through the coil resistance at the switching frequency.As the ratio of coil resistance to inductive reactance increases theefficiency steadily drops. In the limit, where the coil resistancedominates entirely, the fall E/R square wave switching current flows ineach half cycle of the switching, so the full-signal current and theidling current are identical. In this limiting case, the efficiencydrops to that of a Class A amplifier but with much more complicatedcircuitry.

More details about hearing aid receivers can be found in U.S. Pat. No.3,588,383, entitled “Miniature Acoustic Transducer of ImprovedConstruction,” issued to Carlson et al. and U.S. Pat. No. 3,701,865,entitled “Acoustic Transducer Having Diaphragm Pivoted in its Surround,”issued to Carlson et al. Of note, for hearing aid receivers describedtherein, the electrical impedance goes from the DC resistance of thecoil at low frequencies (below approximately 500 Hz) to that of aninductive reactance rising at not quite 6 dB per octave (doubling inreactance for each doubling in frequency).

In Class B applications, an effect of coil resistance is to limit theavailable output at low frequencies for a given drive voltage. Inparticular, the total impedance of an efficient hearing aid receiver canbe effected by resistance at low frequencies. Thus, the doubledresistance of the active half coil can cause a 6 dB reduction in theavailable low-frequency output. If the same amount of (half of theavailable coil) space is devoted to a coil with fewer turns of largerwire, for example 0.707 times the number of turns of wire that is 3 wiresizes larger (0.7 times the Ohms per foot), then the same resistance asa reference full-coil design can be obtained, and the same current willflow through the coil at full output, but the maximum output will havebeen reduced by 3 dB (the same current in 0.7 times the number of turnswill cause 0.7 times the output). This is an improvement over thedouble-resistance loss of 6 dB, but it is still a loss of 3 dB in outputfor the same power from the Class B amplifier. In order to recover thesame sound output available from a full-coil design, the number of turnsmust be dropped to 0.5 times and the wire size increased by 6 wiresizes, resulting in a coil of half the resistance. With this coil, thecurrent for a given voltage will be twice the reference full-coildesign, but the output (Current×turns=magnimotive force=2×current×0.5times turns) will be the same. In order to obtain the same performance,twice the idling current and twice the output current must be applied.Thus, we reach the conclusion that a half-coil-active Class B amplifierdesign as shown in FIG. 2C is only half as efficient at low frequencies,where hearing aid receivers are used.

The type of Class B amplifier shown in FIG. 2C became standard inhigh-power hearing aids for some three decades or more. However, thecircuits shown in FIGS. 2A and 2C both suffer from, among other things,lack of stability, lack of efficiency, or both. After analyzing previouscircuit designs and discovering problems that may have prevented suchcircuits from providing satisfactory performance, the design of a newcircuit was undertaken.

FIG. 3 is a diagram depicting an amplification circuit 601 in accordancewith an embodiment of the present technology. In the embodiment shown inFIG. 3, for example, the Base resistors R9 and R10 in the push-pullstages are split in two, which allows a center point for feedback anddriving. The two resistors in series R9 and R10 perform a similarfunction as the resistor 33 of the Marschinke circuit shown in FIG. 2A.However, rather than rely on the voltage drop that occurs when Basecurrent flows, the sub circuits 603, 604 force DC currents in the Baseresistors R9 and R10 to create voltage drops. This current never entersthe bases, it is withdrawn at the other end of the resistor, therebybiasing the push-pull transistors Q4 and Q10 in a manner thatcompensates for known variables. Similarly, sub circuits 603 and 604provide currents to resistors R12 and R14 to bias push-pull transistorsQ5 and Q11 in sub circuit 615, and the corresponding resistors andtransistors in sub circuit 616.

When the battery is fresh and in the vicinity of about 1.35 Volts, thebiasing current creates a voltage drop acting to maintain the intendedidling currents through the transistors Q4 and Q10. This is accomplishedby sub circuit 603. When the battery drops as low as about 1 Volt, thetransistors Q4 and Q10 would otherwise be turned nearly completely off,except that a bias current in the opposite direction forces a reversedvoltage drop and again maintains the intended idling currents. This isaccomplished by sub circuit 604, which acts to maintain bias intransistors Q5 and Q11 in sub circuit 615 and the correspondingtransistors in sub circuit 616. In certain embodiments, for example,when the battery is around about 1.2 Volts the two sub circuits 603, 604effectively cancel each other out.

Note that the diode-connected transistors Q14 and Q26 in the sub circuit603 can determine the magnitude of the bias reducing current inresistors R12 and R14, as well as R9 and R11 in sub circuit 615 and thecorresponding resistors in sub circuit 616. As the battery voltageincreases, this turn-off current also increases. Also, when VBE isrunning small and/or beta is running high, the push-pull transistorstend to bias harder, and the sub circuit 603 can also run harder andapproximately compensate.

The sub circuit 604 begins with R26 creating a reference current in Q36.This current mirror can be active even as the battery drops well below 1Volt. The action then is to provide, through the mirrors, current thatwill bias up the push-pull stages. However, the reference current in R26can be proportionally stolen as the battery voltage increases to thepoint where the two diode-connected transistors Q25 and Q39 can turn on.

In other words, in the embodiment shown in FIG. 3, for example, circuit601 includes current mirrors that reflect Base-Emitter voltages of biastransistors in sub circuits 603 and 604 in order to provide VBE biasvoltages to driver transistors Q4 and Q10 and output transistors Q5 andQ11 in sub section 615 to provide a Class B output voltage at terminal611. Likewise, driver transistors Q7 and Q13 and output transistors Q6and Q12 in sub section 616 provide a Class B output voltage at terminal612.

Sub section 615 with feedback resistors R3 and R7 can provide 2:1 gainbetween input 610 and output 611. Sub section 616 with feedbackresistors R4, R5, and R6 can provide the complementary output, i.e.provide an output at 612 that is 180 degrees out of phase but otherwisematching the output at 611. In certain embodiments, for example, bothcan provide a low output impedance of less than about 50 Ohms.

Because the Base-Emitter voltages VBE of the transistor in the subcircuits 603 and 604 all have the same temperature coefficient as eachother, e.g. about −2.2 mV per degree C. in certain embodiments, and areon the same die and thus at a nearly identical temperature as thetransistors in amplifier sub circuit 602, an operation relativelyindependent of temperature can be obtained. The operation can beobtained in a manner known in the bipolar circuit art (and illustratedin design of the circuitry used in K-AMP® hearing aids, as described,for example, in U.S. Pat. Nos. 4,170,720 and 5,131,046, which areincorporated herein by reference in their entirety).

For battery voltages above a certain voltage, the sub circuit 603 canprovide a compensatory voltage drop across resistors R9 and R11, andacross R12 and R14, increasing in close approximation to the increase inbattery voltage so that the VBE of transistors Q4 and Q10 and Q5 andQ11, which drive output 611, will be relatively independent of supplyvoltage above that certain voltage. Similarly, the VBE voltages oftransistors Q7 and Q13 and Q6 and Q12 in the sub section driving output612 can similarly be relatively independent of battery voltage.

In sub circuit 603, resistor R24 and diode-connected transistors Q14 andQ26 can provide increasing current to transistors Q15 and Q27 and theyin turn to resistors R12 and R14 as the supply voltage increases, inorder to maintain a nearly constant VBE bias voltage on transistors Q5and Q11 as the supply voltage increases above a certain level. The othertransistors in the sub circuit 603 can similarly provide a nearlyconstant VBE bias voltage, as the supply voltage increases above acertain level, for transistors Q4, Q10, Q6, Q12, Q7, and Q13 in subcircuits 615 and 616. The use of a higher value for R25, which can biasdiode connected transistors Q17 and Q29, than for R24 can compensate forthe higher value of resistors in the sub circuit of the drivertransistors Q4, Q10, Q7, and Q13.

One feature of the circuit 601 is that for battery voltages below acertain voltage, the sub circuit 604 can provide a compensating voltagedrop across the above named resistors in sub section 615 and 616operating to reverse the voltage drop across resistors R9 and R11 andacross R12 and R14 in sub section 615 and their corresponding resistorsin sub section 616. In particular, the sub circuit 604 can maintain theVBEs and thus the idling currents in the two sections at normaloperating values even when the supply voltage drops below the sum of thecorresponding operating VBEs of Q4 plus Q10, etc.

To further explain, the operation of bias transistors Q20-Q23 andQ32-Q35 is to provide current through the aforementioned resistors R9,R11, R12 and R14 in sub circuit 615 (and the corresponding resistors insub circuit 616) flowing from the positive supply through first resistorR11 and then R9, for example, to the negative rail (chip ground). Thiscurrent is arranged to increase as the supply voltage decreases,providing the Base-Emitter bias voltage required for proper operationeven when the supply voltage falls below the sum of the Base-Emittervoltages. In certain embodiments, it has been found adequate to increasethe size of the bias transistors feeding the output stage transistors inorder to provide the required compensating bias voltage as the supplydrops below a certain voltage.

In order to avoid conflict between operation of sub circuits 603 and604, the operation of resistor R27 with transistors Q25, Q39, and Q38 insub circuit 604 is to disable the operation of sub circuit 604 above acertain supply voltage by effectively removing the collector voltagefrom bias transistor Q37 so that sub circuit 604 does not affect thefunctioning of circuit 601 above a certain supply voltage.

In certain embodiments, for example, the circuit 601 can provide arelatively low-cost, low-distortion, high-efficiency amplifier suitablefor use with two-terminal receivers in hearing aids and otherlow-voltage applications. Further, in certain embodiments, for example,the circuit 601 can provide an integrated circuit Class B output drivethat can operate with low idling current and low distortion that isalmost independent of temperature and supply voltage over the range ofabout 1.0 to about 1.4 Volts. In certain embodiments, for example, thecircuit 601 can be used in a hearing aid and can provide a battery lifethat is 3-10 times that available from many existing digital hearingaids.

As described below, certain embodiments of the present technologyprovide hearing aids that include the circuit 601 described above. Inother embodiments, for example, the circuit described above can be usedin connection with other devices, as will be appreciated by thoseskilled in the art after reviewing this disclosure.

FIG. 4 is a diagram 500 depicting circuitry and components of a hearingaid. The components include a microphone 502, a battery 504, and anamplification circuit 506. The microphone 502 is shown connected to theregulated supply, but it will be readily understood that suchmicrophones have an output terminal that is connected to the IN terminalof the circuit 508 of FIG. 4, and a ground terminal that is connected tothe GND terminal of circuit 508. The amplification circuit 506 includescircuitry 508 and circuitry 510. Circuitry 508 can include the elementsshown, which elements are described in further detail in U.S. Pat. No.5,131,046, entitled “High Fidelity Hearing Aid Amplifier,” which issuedto Killion et al. and is incorporated herein by reference in itsentirety. Such circuitry is that which is used in K-AMP® hearing aidsdescribed previously. Circuitry 510 can include the circuit 601described above in connection with FIG. 3. Such a configuration waspreviously unavailable because no suitable Class B output circuit wasavailable to operate properly in combination with the circuitry used inK-AMP® hearing aids in order to provide long battery life. Further, incertain embodiments, circuitry 508 and circuitry 510 can be implementedas an integrated circuit.

In the embodiment shown in FIG. 4, for example, the battery 504 canprovide power for a hearing aid. The microphone 502 can receive ambientsound and convert the sound into electrical signals. The electricalsignals can be communicated to the amplification circuit 506. Theamplification circuit 506 can be configured to process received signalsin many ways, some of which are described below. The amplificationcircuit 506 can communicate processed signals to a two-terminal receivervia outputs 512. The receiver can convert the processed signals intosound and communicate the sound to a user of the hearing aid.

The embodiment shown in FIG. 4, for example, provides an analog hearingaid with Class B amplifier that can provide the sound quality of K-AMP®hearing aids without the cost associated with Class D amplifiers. Incertain embodiments, for example, the hearing aid can provide frequencyresponse accuracy of at least about 80 percent. The shown embodiment canalso reduce costs by eliminating the need for a three-wire receivertraditionally used in connection with Class B hearing aid circuits.Further, in certain embodiments, the low idling current associated withthe Class B amplifier can provide for extended battery life. In certainembodiments, for example, the hearing aid can provide for battery drainof less than about 0.5 mA.

In certain embodiments, for example, with a 312 zinc air cell, a batterylife of three weeks can be provided. In certain embodiments, forexample, with a 13A zinc air cell, a battery life of 5 weeks can beprovided. This is in sharp contrast to the 3 days to 10 days batterylife typical for many digital hearing aids.

FIG. 5A is a diagram depicting hearing aid components 200 used inaccordance with an embodiment of the present technology. The components200 include switch 202, amplification circuit 208, microphone 210,battery 212 and receiver 214. Battery 212 provides power. Microphone 210converts sound to electrical signals and communicates the signals to theamplification circuit 208. Amplification circuit 208 can process thesignals. In certain embodiments, for example, the amplification circuit208 can be configured in the same manner as the amplification circuit506 described in connection with FIG. 4. Amplification circuit 208 cancommunicate the processed signals to the receiver 214, which can convertthe signals to sound. Switch 202 includes a first setting 204 configuredto provide high gain and a second setting 206 configured to provide lowgain. Switch 202 is in communication with amplification circuit 208 viaresistors R1 and R2. In certain embodiments, for example, a low gainsetting can provide about 15 db of high-frequency insertion gain(real-ear gain) for quiet sounds and about 0 dB insertion gain for loudsounds, which are passed through as if the hearing aid was not there. Incertain embodiments, for example, a high gain setting can provide about23 db of high-frequency insertion gain (real-ear gain) for quiet soundsand about 8 dB insertion gain for loud sounds. In such embodiments, forexample, quiet sounds can be sounds below about 50-60 dB and loud soundscan be sounds above about 85-90 dB. In certain embodiments, for example,quiet and loud sounds can be specified at other levels. In certainembodiments, for example, sounds between the quiet sound ceiling and theloud sound floor can receive proportional amplification, wherein every 2dB increase of input sound results in a 1 dB increase in amplification.In certain embodiments, for example, sounds between the quiet soundceiling and the loud sound floor can receive proportional amplificationat other levels.

FIG. 5B is a diagram depicting hearing aid components 300 used inaccordance with an embodiment of the present technology. The components300 include volume controller 302, amplification circuit 208, microphone210, battery 212 and receiver 214. Battery 212 provides power.Microphone 210 converts sound to electrical signals and communicates thesignals to the amplification circuit 208. Amplification circuit 208 canprocess the signals. In certain embodiments, for example, theamplification circuit 208 can be configured in the same manner as theamplification circuit 506 described in connection with FIG. 4.Amplification circuit 208 can communicate the processed signals to thereceiver 214, which can convert the signals to sound. Volume controller302 can provide for increasing and decreasing the volume of soundprovided by the receiver 214. Volume controller 302 is in communicationwith amplification circuit 208 via resistor 304. In certain embodiments,for example, by suitable choice of the value of resistance in volumecontroller 302 and the resistance of resistor 304, a range ofhigh-frequency gain for quiet sounds from about 5 dB to about 23 dB canbe obtained, with a corresponding range of gain for loud sounds of about−10 dB to about +8 dB. In such embodiments, for example, quiet soundscan be sounds below about 50-60 dB and loud sounds can be sounds aboveabout 85-90 dB. In certain embodiments, for example, quiet and loudsounds can be specified at other levels. In certain embodiments, forexample, sounds between the quiet sound ceiling and the loud sound floorcan receive proportional amplification, wherein every 2 dB increase ofinput sound results in a 1 dB increase in amplification. In certainembodiments, for example, sounds between the quiet sound ceiling and theloud sound floor can receive proportional amplification at other levels.The ability to attenuate loud sounds can be useful in some circumstanceswhere the wearer needs hearing protection but because of his or herhearing loss is reluctant to wear it. With the configuration shown inFIG. 5B, for example, it is possible to provide protection from loudsounds while still providing a small amount of high-frequency gain forquiet sounds.

FIG. 6A is a top view of a hearing aid 400 used in accordance with anembodiment of the present technology. FIGS. 6B and 6C are side views ofthe hearing aid 400 depicted in FIG. 6A. FIG. 6D is a side sectionalview of the hearing aid 400 about the line A-A of FIG. 6B. FIG. 6E is aside view of the hearing aid 400 depicted in FIG. 6A with an ear tip 406attached thereto. The hearing aid 400 includes a housing 402 comprisinga first end 404 configured to receive a removable ear tip 406 (shown inFIG. 6E). The first end 404 includes a sound port 410. When the hearingaid 400 is inserted into a user's ear, the first end 404 is insertedinto the user's ear canal such that sound may be communicated to the earcanal from the sound port 410 via the ear tip 406. The housing 400 alsoincludes a second end 408 opposite the first end 404. A handle 412 isdisposed on the second end 408. The handle 412 extends from the secondend 408 and is configured to facilitate insertion and removal of thehearing aid 400. The second end 408 includes a sound port 414 configuredto receive a microphone 416. When the hearing aid 400 is inserted into auser's ear, the second end 408 faces away from the user's ear canal suchthat ambient sound can be communicated to the microphone 416. The secondend 408 also includes a switch 418 movable between a first position anda second position. In certain embodiments, for example, the switch 418and other components of the hearing aid 400 can be configured as shownand described in FIG. 5A. As shown in FIG. 6D, disposed inside thehousing 402 is the microphone 416, wiring 420, 430, resistors 428,battery 422, amplification circuit 426, and receiver 424. Sound receivedat the microphone 416 is converted to electrical signals that areprocessed by the amplification circuit 426. The amplification circuit426 provides processed signals to the receiver 424, which converts thesignals into sound. Sound passes from the receiver 424 via sound port410 and through the ear tip 406 (shown in FIG. 6E). While passingthrough the ear tip 406, the sound passes through a damper 430 mountedwith and disposed within the ear tip 406. In certain embodiments, forexample, the damper 430 can be a commercially available damper, such asthe ER-4S damper made by Etymotic Research, Inc., for example, and/or acommercial embodiment of the dampers described in U.S. Pat. Nos.6,666,295 and 6,830,876, issued to Killion et al., the content of whichpatents is incorporated herein by reference in their entirety. Incertain embodiments, for example, the damper 430 can smooth frequencyresponse.

Applicants have found that it is common to provide hearing aids withoutsmooth frequency response, even in expensive hearing aids, as indicatedby the low fidelity illustrated in FIGS. 1A, 1B, and 1C. This despiteapplicant Killion's description in several publications of a means forproviding a high fidelity frequency response by a combination ofselected sound channel dimensions forming “acoustical horns” (sometimesinformally called “earmold plumbing”) and acoustical damping element orelements to smooth the response peaks. See, for example, Killion M C,“Earmold Plumbing for Wideband Hearing Aids,” J. Acoust. Soc. Am. 59,562(A), 1976, available from Knowles Electronics, Franklin Park, Ill.,and Killion M C and Tillman T W, “Evaluation of high-fidelity hearingaids,” J. Speech Hearing Res. 25, 15-25, 1982. FIG. 6L illustrates theimprovement brought about by applying these techniques. In FIG. 6L,taken from the latter reference, the dotted line depicts the frequencyresponse of conventional earmolds, and the solid line depicts thefrequency response of earmolds that apply the techniques discussedabove. U.S. Pat. Nos. 4,852,683 and 5,113,967, which issued to Killionand Killion et al., respectively, also relate to using damping to smoothfrequency response.

Applicant Killion later described electronic means of smoothing thefrequency response using “electronic damping” wherein the inverse of adamping peak was programmed into the hearing aid amplifier. See, forexample, U.S. Pat. No. 5,812,679, entitled “Electronic Damper Circuitfor a Hearing Aid and a Method of Using the Same,” issued to Killion etal. and U.S. Pat. Nos. 6,047,075 and 6,466,678, both issued to Killionet al. Here, again, the frequency response of some digital hearing aidssuggest that neither method is being used.

In order to provide a low-cost high-fidelity hearing aid, electronicdamping may be considered impractical due to the associated cost.However, applicants have found that replaceable dampers, such as theER-4S dampers made by Etymotic Research, Inc., for example, can be usedin hearing aids and are relatively cheaper.

Applicants have also found that a problem exists, wherein sublimatedearwax in some wearers can clog the pores of a damping element. In somecases, a dispenser may simply remove the damper or send the hearing aidin for repair. As discussed below, certain embodiments of the presenttechnology provide hearing aids with replaceable dampers that areconfigured to block debris from entering a hearing aid.

FIG. 6F is a side view of an ear tip 406 used in accordance with anembodiment of the present technology. FIG. 6G is a side sectional viewof the ear tip 406 shown in FIG. 6F about the line A-A. As shown, theear tip 406 includes a plurality of flanges. The ear tip 406 alsoincludes a damper 432 mounted with the ear tip 406 and disposed withinthe sound path 434 of the ear tip 406. The damper 430 includes a meshfilter 432 that can provide a debris barrier. For example, the filter432 can block ear wax and/or other debris form entering a hearing aidthrough the ear tip 406.

FIG. 6H is a side view of an ear tip 450 used in accordance with anembodiment of the present technology. FIG. 6I is a side sectional viewof the ear tip 450 shown in FIG. 6H about the line A-A. As shown, theear tip 450 comprises an ear plug 452 with a sound path 454therethrough. The ear tip 450 also includes a damper 432 mounted withthe ear tip 450 and disposed within the sound path 454 of the ear tip450. The damper 430 includes a mesh filter 432 that can provide a debrisbarrier. For example, the filter 432 can block ear wax and/or otherdebris form entering a hearing aid through the ear tip 450.

FIG. 6J is a side view of a hearing aid 460 used in accordance with anembodiment of the present technology. FIG. 6K is a side sectional viewof the hearing aid 460 shown in FIG. 6J. The hearing aid 460 is the sameas the hearing aid 400 described previously except that the hearing aid460 includes the damper 430 mounted with and disposed within the housing402 rather than mounted with and disposed within the ear tip. Likewise,the hearing aid 460 can be used with an ear tip 462 that does notinclude a damper disposed therein.

FIG. 7A is top view of a hearing aid 700 used in accordance with anembodiment of the present technology. FIGS. 7B and 7C are side views ofthe hearing aid 700 depicted in FIG. 7A. FIG. 7D is a side sectionalview of the hearing aid 700 about the line A-A of FIG. 7B. FIG. 7E is aside view of the hearing aid 400 depicted in FIG. 6A with an ear tip 406attached thereto. FIGS. 7A-7E depict a hearing aid 700 with many of thesame elements as the hearing aid 400 shown and described in connectionwith FIGS. 6A-6E. However, the hearing aid 700 includes a volumecontroller 702 rather than a switch 418. In certain embodiments, forexample, the volume controller 702 and other components of the hearingaid 700 can be configured as shown and described in FIG. 5B.

FIG. 7F is a side view of a hearing aid 760 used in accordance with anembodiment of the present technology. FIG. 7G is a side sectional viewof the hearing aid 760 shown in FIG. 6J. The hearing aid 760 is the sameas the hearing aid 700 described above except that the hearing aid 760includes the damper 430 mounted with and disposed within the housing 402rather than mounted with and disposed within the ear tip. Likewise, thehearing aid 460 can be used with an ear tip 462 that does not include adamper disposed therein.

FIG. 8A illustrates a one-size-fits-most hearing aid 800, in accordancewith an embodiment of the present technology. FIG. 8B illustrates a sideview of the hearing aid 800 of FIG. 8A with the battery sleeve 840retracted. In certain embodiments, for example, the hearing aid 800 caninclude similar elements and similar functionality as the hearing aidsdescribed in U.S. patent application Ser. No. 11/031,915, filed Jan. 7,2005 and published as 2005/0147267, which patent application is herebyincorporated herein by reference in its entirety.

In an embodiment, the hearing aid 800 may comprise a triple-flangeeartip 880 attached to a cylindrical housing 830 containing areplaceable battery, a microphone, an amplifier, a receiver to reproducethe amplified sound, and a switch. In certain embodiments, the amplifiercan include an amplification circuit like the amplification circuits506, 208, 426 described above. Other hearing aid components, such as themicrophone, battery and receiver, for example, can also be configuredlike the components described above. In certain embodiments, forexample, the eartip 880 can include a damper 430 with filter 432 asdescribed above. In such embodiments, the damper 430 can be replaced byreplacing the eartip 880. In certain embodiments, for example, a damper430 with filter 432 can be mounted with and disposed in the housing 830such that the damper 430 can be removed and replaced by simply removingan eartip.

In the embodiment shown in FIGS. 8A and 8B, for example, hearing aid 800has a generally cylindrical shape. A battery sleeve 840 and main body orhousing 830 are also be cylindrical. The battery sleeve 840 may beclosed as in 8B, and in such an embodiment the hearing aid 800 may beworn by the user. When, for example, the user may want to replace thebattery 844, the battery sleeve 840 may be retracted, and the batteryslot 842 may be exposed and the battery 844 may be removed and replaced.The battery slot 842 may be defined by the sides 839, which may beattached to the hearing aid main body or housing 830. In certainembodiments, an old battery 844 need not be removed, instead a newbattery may replace the old battery by simply inserting the new batteryinto the battery slot in any of the four possible positions, and doingso forces the old battery to be disposed of automatically from the otherside.

In the embodiment shown in FIGS. 8A and 8B, for example, eartip 880 mayhave rotational symmetry around its axis and the axis of the hearing aid800. In particular, eartip flanges 884, 885, and 886 and eartip stem 882may all be generally round. The use of the three eartip flanges 884,885, and 886 may increase the percentage of persons who can obtain agood comfortable seal in the ear canal. The eartip flanges 884, 885, and886 are in a decreasing size, whereas the smallest flange 886 is closestto the tip of the hearing aid 800, and the largest flange 884 isfarthest away from the tip of the hearing aid 800. Consequentially, ifthe smallest flange 884 does not seal the ear canal well, the slightlylarger flange 885 may do so, and if the flange 885 also does notcompletely seal the ear canal, the largest flange 886 may do so, thusensuring a comfortable and good seal of the ear canal for a largernumber of users than if one flange were used. Ensuring a good seal tothe ear canal for a hearing aid generally provides a good performance,because, for example, it prevents unwanted audio feedback of sounds,which may interfere with the sounds coming into the hearing aid.

FIG. 9A illustrates a perspective view of a hearing aid 900 used inaccordance with an embodiment of the present technology. FIG. 9B depictsthe hearing aid 900 of FIG. 9A in an operative position on a user 950.FIG. 9C depicts the hearing aid 900 of FIG. 9A and a boom/microphoneassembly 906 that can be used therewith in accordance with an embodimentof the present technology. To some users, the hearing aid 900 with orwithout the boom/microphone assembly 906 may be considered moreaesthetically pleasing than other designs.

In the embodiment shown in FIG. 9A, the hearing aid 900 includes ahousing 901 comprising a first end 905 with a port 904 extendingtherefrom. The port 904 is configured to receive a removable eartip 903.When the hearing aid 900 is inserted into a user's ear, the eartip 903is inserted into the user's ear canal such that sound may becommunicated to the ear canal from the hearing aid 900. The housing 901also includes a second end 902 opposite the first end 905. The secondend 902 includes a sound port 908 configured to receive ambient sound. Amicrophone is disposed in the housing 901 such that it can receiveambient sound via the sound port 908. When the hearing aid 900 isinserted into a user's ear, the second end 902 is outside the ear canalsuch that ambient sound can be communicated to the microphone.

In certain embodiments, for example, the hearing aid 900 can include abattery, microphone, amplification circuit, and receiver configured likethose described above in connection with other embodiments. Further, incertain embodiments, for example, the hearing aid 900 can include aswitch or volume controller as described above in connection with otherembodiments. The microphone can convert ambient sound into electricalsignals that are processed by the amplification circuit, then thereceiver can convert the electrical signal into sound. Sound can bepassed through port 904, a damper, and eartip 903 and into the ear canalof a user. In certain embodiments, the eartip 903 can provide anacoustic seal of the ear canal. In certain embodiments, for example, theeartip can include a damper 430 with filter 432 as described above. Insuch embodiments, the damper 430 can be replaced by replacing theeartip. In certain embodiments, for example, a damper 430 with filter432 can be mounted with and disposed in the port 904 such that thedamper 430 can be removed and replaced by simply removing an eartip.

In certain embodiments, such as the embodiment shown in FIG. 9C, forexample, the hearing aid 900 can include a directional microphone 911 ina boom/microphone assembly 906 that is attachable to the housing 901. Insuch embodiments, for example, experiments show that an improvement insignal-to-noise ratio of about 6 dB can be obtained compared to themicrophone disposed on the housing 901. Either microphone can receivesound, convert the sound into electrical signals.

In certain embodiments, for example, providing a hearing aid 900 asdescribed above can provide a low-cost, non-digital hearing aid.Further, in certain embodiments, for example, providing a hearing aid900 as described above can provide a battery life of at least 7 daysbetween charges. Also, in certain embodiments, for example, providing ahearing aid 900 as described above using a down converter as opposed toa silicon diode may provide increased battery life.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

1. An amplification circuit comprising: a first sub circuit configuredto create a voltage drop when a supply voltage is above a first voltage;and a second sub circuit configured to create a reverse voltage dropwhen the supply voltage is below a second voltage, wherein the first andsecond sub circuits operate to maintain idling current within a range.2. The amplification circuit of claim 1, wherein the voltage drop isacross a plurality of resistors such that a base emitter voltage of aplurality of transistors is independent of supply voltage above thefirst voltage.
 3. The amplification circuit of claim 1, wherein thereverse voltage drop is across a plurality of resistors such that a baseemitter voltage of a plurality of transistors is independent of supplyvoltage below the second voltage.
 4. The amplification circuit of claim1, wherein the second sub circuit is disabled when the supply voltage isabove a third voltage.
 5. The amplification circuit of claim 4, whereinthe first voltage is about volts, the second voltage is about 1 volt,and the third voltage is about 1.2 volts.
 6. The amplification circuitof claim 1, wherein the first sub circuit and the second sub circuit areprovided on the same die and have the same temperature coefficient. 7.The amplification circuit of claim 1, further comprising: a first outputand a second output, wherein the outputs are configured to be used witha two-terminal receiver.
 8. The amplification circuit of claim 7,wherein the second output is configured to provide an output that is 180degrees out of phase with the output provided by the first output. 9.The amplification circuit of claim 8, wherein the circuit provides anoutput without the use of output capacitors.
 10. The amplificationcircuit of claim 1, wherein the circuit is configured to be used in ahearing aid.
 11. A method for maintaining idling current of anamplification circuit within a range, the method comprising: creating avoltage drop when a supply voltage is above a first voltage; andcreating a reverse voltage drop when the supply voltage is below asecond voltage.
 12. The method of claim 11, wherein the voltage drop isacross a plurality of resistors such that a base emitter voltage of aplurality of transistors is independent of supply voltage above thefirst voltage, and wherein the reverse voltage drop is across aplurality of resistors such that a base emitter voltage of a pluralityof transistors is independent of supply voltage below the secondvoltage.
 13. A hearing aid comprising: a housing; a microphoneconfigured to convert ambient sound into electrical signals; anamplification circuit configured to process electrical signals receivedfrom the microphone; a receiver configured to convert processed signalsreceived from the amplification circuit into sound; and a removabledamper configured to smooth the frequency response of sound provided bythe receiver.
 14. The hearing aid of claim 13, wherein the damper ismounted with the housing.
 15. The hearing aid of claim 13, furthercomprising an eartip configured to be removably attached to the housing,wherein the damper is mounted with the eartip.
 16. The hearing aid ofclaim 13, wherein the damper includes a filter configured to blockdebris.
 17. The hearing aid of claim 13, wherein frequency responseaccuracy is at least 80 percent.
 18. The hearing aid of claim 13,further including a battery, wherein the battery drain is less than 0.5mA.
 19. The hearing aid of claim 13, farther comprising a switchoperably connected to the amplification circuit, wherein the switch isconfigured to provide gain at a first setting and a second setting. 20.The hearing aid of claim 19, wherein the first setting can provide atleast about 15 dB of gain for quieter sounds and about 0 dB of gain forlouder sounds, wherein the second setting can provide at least about 23dB of gain for quieter sounds and about 8 dB of gain for louder sounds,and wherein quieter sounds are sounds below about 50-60 dB and loudersounds are sounds above about 85-90 dB.
 21. The hearing aid of claim 13,further comprising a volume controller operably connected to theamplification circuit, wherein the volume controller is configured toprovide for increasing and decreasing gain.
 22. The hearing aid of claim21, wherein the volume controller is configured to provide a range ofgain for quieter sounds from about 5 dB to about 23 dB and acorresponding range of gain for louder sounds from about −10 dB to about8 dB, and wherein quieter sounds are sounds below about 50-60 dB andlouder sounds are sounds above about 85-90 dB.
 23. The hearing aid ofclaim 13, wherein the amplification circuit includes: a first subcircuit configured to create a voltage drop when a supply voltage isabove a first voltage; and a second sub circuit configured to create areverse voltage drop when the supply voltage is below a second voltage,wherein the first and second sub circuits operate to maintain idlingcurrent within a range.